Maximizing Use of Storage in a Data Replication Environment

ABSTRACT

Mechanisms for controlling access to storage volumes on the secondary storage system is provided. A determination is made as to whether a first site computing device has sent a notification of a failure condition of a first site. In response to a determination that the notification of the failure condition of the first site has not been received, secondary workloads of a second site computing device are permitted to access storage volumes on the secondary storage system. In response to a determination that the notification of the failure condition of the first site has been received, a mode of operation of the second site is modified from a normal mode of operation to a failure mode of operation. In the failure mode of operation, the storage system controller of the second site blocks at least a portion of access requests from secondary workloads of the second site computing device.

BACKGROUND

The present application relates generally to an improved data processingapparatus and method and more specifically to mechanisms for maximizingthe use of storage system resources in a data replication environment.

Data replication across storage systems is used to provide protectionand continued access to data for disaster recovery. The primary datavolumes are used for read/write access by attached host systems. Updatesto the primary volumes are replicated to a set of secondary data volumesin a separate storage device/system. The storage device/systems thatprovide the primary and secondary data volumes are physically separateand are likely at different geographic sites. If a set of primary datavolumes at a site storage device/system is unavailable for any reason,there are mechanisms to transition work from the primary data volumes tothe secondary data volumes at the other site. Ideally, this transitionis accomplished without impacting performance required by workloadsbeing submitted to the primary data volumes which are now transitionedto the secondary data volumes at the alternate site. This means that thesecondary storage devices/system of the alternate site is significantlyunder-utilized to ensure that it can meet performance requirements inthe event of a failover from the primary workload.

SUMMARY

In one illustrative embodiment, a method, in a data processing systemcomprising a first storage system controller and a second storagesystem, for controlling access to storage volumes on the second storagesystem is provided. The method comprises determining, by the storagesystem controller, whether a first site computing device has sent anotification of a failover condition for accessing primary data volumesat a first site. The method further comprises, in response to adetermination that the notification of the failover condition of theprimary volumes at a first site has not been received, permitting, bythe storage system controller, other workloads of a second sitecomputing device to access storage volumes on the second storage system.Moreover, the method also comprises, in response to a determination thatthe notification of the failover condition of the first site primaryvolumes has been received, modifying, by the storage system controller,a mode of operation of the second site from a normal mode of operationto a failover mode of operation. In the failover mode of operation, thestorage system controller of the second site blocks or lowers priorityof at least a portion of access requests from local or non-criticalworkloads of the second site computing devices.

In other illustrative embodiments, a computer program product comprisinga computer useable or readable medium having a computer readable programis provided. The computer readable program, when executed on a computingdevice, causes the computing device to perform various ones of, andcombinations of, the operations outlined above with regard to the methodillustrative embodiment.

In yet another illustrative embodiment, a system/apparatus is provided.The system/apparatus may comprise one or more processors and a memorycoupled to the one or more processors. The memory may compriseinstructions which, when executed by the one or more processors, causethe one or more processors to perform various ones of, and combinationsof, the operations outlined above with regard to the method illustrativeembodiment.

These and other features and advantages of the present invention will hedescribed in, or will become apparent to those of ordinary skill in theart in view of, the following detailed description of the exampleembodiments of the present invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention, as well as a preferred mode of use and further objectivesand advantages thereof, will best be understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is an example diagram of a distributed data processing system inwhich aspects of the illustrative embodiments may be implemented;

FIG. 2 is an example block diagram of a computing device in whichaspects of the illustrative embodiments may be implemented;

FIG. 3A illustrates the replication pair of a first site A and a secondsite B as part of a peer-to-peer remote copy (PPRC), or other failovermechanism, prior to a failure of the first site A in accordance with oneillustrative embodiment;

FIG. 3B illustrates the replication pair of a first site A and a secondsite B as part of a peer-to-peer remote copy (PPRC), or other failovermechanism, after a failure of the first site A in accordance with oneillustrative embodiment;

FIG. 3C is an example block diagram illustrating the use of failovermechanisms for increasing utilization of secondary storage systems inaccordance with another illustrative embodiment;

FIG. 4 is a flowchart outlining an example operation for implementing afailover mechanism in accordance with one illustrative embodiment; and

FIG. 5 is a flowchart outlining an example operation for implementingfailover mechanism in accordance with another illustrative embodiment

DETAILED DESCRIPTION

The illustrative embodiments provide mechanisms for maximizing the useof storage system resources in a data replication environment. A firstsite storage system provides the primary data volumes for read/writeaccess by a set of host systems and writes replication data to a secondsite storage system which provides a secondary set of data volumes thatstore a copy of the first site primary volumes.

With the mechanisms of the illustrative embodiments, the second sitestorage system is configured to permit utilization of the entire secondsite storage system, or at least the majority of the second site storagesystem, during times when the second site storage system is not thetarget of a failover, i.e. while the first site storage system (storagesystem with the primary data volumes of a replication pair) isfunctioning in a normal, non-failover, mode of operation. Volumes on thesecond site storage system have associated volume attributes thatspecify which volumes are accessible by non-critical workloads duringnormal, i.e. non-failover, operation and which volumes are accessible bynon-critical workloads during non-normal, i.e. failover, modes ofoperation. During a failover condition, the volumes that were accessibleto non-critical workloads during normal operation are no longeraccessible to these non-critical workloads, or at least a majority ofthese volumes will not be accessible to the non-critical workloads, andinstead only the secondary volumes associated with the first site'sprimary volume workloads are accessible. Moreover, all of the resourcesof the second site storage system are then made available to the firstsite's workloads during the failover condition.

Thus, with the mechanisms of the illustrative embodiments, storagevolumes in a second site storage system at a second site are providedthat are only usable by non-critical workloads if the first site and theprimary data volumes in the first site storage system at the first siteare functioning normally, i.e. a non-failover condition. Thesenon-critical volumes are made unavailable on failover, thereby causingall non-critical work to be halted and the system resources of thesecond site storage system are made available to meet the first siteprimary data volume workload requirements. As a result, the second sitestorage system is able to run a set of non-critical applications whileassuring the first site storage system and first site the ability toprovide full throughput to the primary data volume workloads in the caseof a failover condition.

In another illustrative embodiment, rather than discontinuing allnon-critical applications in the event of a failover, the mechanisms ofthe illustrative embodiments may transfer volume priority settings ofthe primary data volumes from the first site storage system to thesecond site storage system and apply the transferred volume prioritysettings to all workloads, both primary data volume workloads and secondsite workloads, being handled by the second site storage system. Thismay include merging the volume priority settings of the primary datavolumes from the first site storage system with the existing volumepriority settings of the volumes in the second site storage system andresolving any conflicts in the two different sets of volume prioritysettings.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method, or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in any one or more computer readablemedium(s) having computer usable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CDROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, in abaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Computer code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, radio frequency (RF), etc., or anysuitable combination thereof.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java™, Smalltalk™, C++, or the like, and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoft-ware package, partly on the user's computer and partly on a remotecomputer, or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to the illustrativeembodiments of the invention. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions thatimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus, or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment., or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

Thus, the illustrative embodiments may be utilized in many differenttypes of data processing environments. In order to provide a context forthe description of the specific elements and functionality of theillustrative embodiments, FIGS. 1 and 2 are provided hereafter asexample environments in which aspects of the illustrative embodimentsmay be implemented. It should be appreciated that FIGS. 1 and 2 are onlyexamples and are not intended to assert or imply any limitation withregard to the environments in Which aspects or embodiments of thepresent invention may be implemented. Many modifications to the depictedenvironments may be made without departing from the spirit and scope ofthe present invention.

FIG. 1 depicts a pictorial representation of an example distributed dataprocessing system in which aspects of the illustrative embodiments maybe implemented. Distributed data processing system 100 may include anetwork of computers in which aspects of the illustrative embodimentsmay be implemented. The distributed data processing system 100 containsat least one network 102, which is the medium used to providecommunication links between various devices and computers connectedtogether within distributed data processing system 100. The network 102may include connections, such as wire, wireless communication links, orfiber optic cables.

In the depicted example, server 104 and server 106 are connected tonetwork 102 along with storage unit 108. Furthermore, servers 104 and106 may also have their own associated storage devices/systems 105 and107. In addition, clients 110, 112, and 114 are also connected tonetwork 102. These clients 110, 112, and 114 may be, for example,personal computers, network computers, or the like. In the depictedexample, server 104 provides data, such as boot files, operating systemimages, and applications to the clients 110, 112, and 114. Clients 110,112, and 114 are clients to server 104 in the depicted example.Distributed data processing system 100 may include additional servers,clients, and other devices not shown.

In the depicted example, distributed data processing system 100 is theInternet with network 102 representing a worldwide collection ofnetworks and gateways that use the Transmission ControlProtocol/Internet Protocol (TCP/IP) suite of protocols to communicatewith one another. At the heart of the Internet is a backbone ofhigh-speed data communication lines between major nodes or hostcomputers, consisting of thousands of commercial, governmental,educational and other computer systems that route data and messages. Ofcourse, the distributed data processing system 100 may also beimplemented to include a number of different types of networks, such asfor example, an intranet, a local area network (LAN), a wide areanetwork (WAN), or the like. As stated above, FIG. 1 is intended as anexample, not as an architectural limitation for different embodiments ofthe present invention, and therefore, the particular elements shown inFIG. 1 should not be considered limiting with regard to the environmentsin which the illustrative embodiments of the present invention may beimplemented.

FIG. 2 is a block diagram of an example data processing system in whichaspects of the illustrative embodiments may be implemented. Dataprocessing system 200 is an example of a computer, such as client 110 inFIG. 1, in which computer usable code or instructions implementing theprocesses for illustrative embodiments of the present invention may belocated.

In the depicted example, data processing system 200 employs a hubarchitecture including north bridge and memory controller hub (NB/MCH)202 and south bridge and input/output (I/O) controller hub (SB/ICH) 204.Processing unit 206, main memory 208, and graphics processor 210 areconnected to NB/MCH 202. Graphics processor 210 may be connected toNB/MCH 202 through an accelerated graphics port (AGP).

In the depicted example, local area network (LAN) adapter 212 connectsto SB/ICH 204. Audio adapter 216, keyboard and mouse adapter 220, modem222, read only memory (ROM) 224, hard disk drive (HDD) 226, CD-ROM drive230, universal serial bus (USB) ports and other communication ports 232,and PCI/PCIe devices 234 connect to SB/ICH 204 through bus 238 and bus240. PCI/PCIe devices may include, for example, Ethernet adapters,add-in cards, and PC cards for notebook computers. PCI uses a card buscontroller, while PCIe does not. ROM 224 may be, for example, a flashbasic input/output system (BIOS).

HDD 226 and CD-ROM drive 230 connect to SB/ICH 204 through bus 240. HDD226 and CD-ROM drive 230 may use, for example, an integrated driveelectronics (IDE) or serial advanced technology attachment (SATA)interface. Super I/O (SIO) device 236 may be connected to SB/ICH 204.

An operating system runs on processing unit 206. The operating systemcoordinates and provides control of various components within the dataprocessing system 200 in FIG. 2. As a client, the operating system maybe a commercially available operating system such as Microsoft® Windows7®. An object-oriented programming system, such as the Java™ programmingsystem, may run in conjunction with the operating system and providescalls to the operating system from Java™ programs or applicationsexecuting on data processing system 200.

As a server, data processing system 200 may be, for example, an IBM®eServer™ System p® m computer system, running the Advanced InteractiveExecutive (AIX®) operating system or the LINUX® operating system. Dataprocessing system 200 may be a symmetric multiprocessor (SMP) systemincluding a plurality of processors in processing unit 206.Alternatively, a single processor system may be employed.

Instructions for the operating system, the object-oriented programmingsystem, and applications or programs are located on storage devices,such as HDD 226, and may be loaded into main memory 208 for execution byprocessing unit 206. The processes for illustrative embodiments of thepresent invention may be performed by processing unit 206 using computerusable program code, which may be located in a memory such as, forexample, main memory 208, ROM 224, or in one or more peripheral devices226 and 230, for example.

A bus system, such as bus 238 or bus 240 as shown in FIG. 2, may becomprised of one or more buses. Of course, the bus system may beimplemented using any type of communication fabric or architecture thatprovides for a transfer of data between different components or devicesattached to the fabric or architecture. A communication unit, such asmodem 222 or network adapter 212 of FIG. 2, may include one or moredevices used to transmit and receive data. A memory may be, for example,main memory 208, ROM 224, or a cache such as found in NB/MCH 202 in FIG.2.

Those of ordinary skill in the art will appreciate that the hardware inFIGS. 1 and 2 may vary depending on the implementation. Other internalhardware or peripheral devices, such as flash memory, equivalentnon-volatile memory, or optical disk drives and the like, may be used inaddition to or in place of the hardware depicted in FIGS. 1 and 2. Also,the processes of the illustrative embodiments may be applied to amultiprocessor data processing system, other than the SMP systemmentioned previously, without departing from the spirit and scope of thepresent invention.

Moreover, the data processing system 200 may take the form of any of anumber of different data processing systems including client computingdevices, server computing devices, a tablet computer, laptop computer,telephone or other communication device, a personal digital assistant(PDA), or the like. In some illustrative examples, data processingsystem 200 may be a portable computing device that is configured withflash memory to provide non-volatile memory for storing operating systemfiles and/or user-generated data, for example. Essentially, dataprocessing system 200 may be any known or later developed dataprocessing system without architectural limitation.

With reference again to FIG. 1, a peer-to-peer copy (PPRC) or otherfailover mechanism may be established between a first site A 120, e.g.,server 104, and a second site B 130, e.g., server 106. The failovermechanism may cause data/applications to be replicated on both the firstsite A 120 and the second site B 130 during normal operation and/or inresponse to a detected failure or imminent failure. For example, in somefailover mechanisms, the first site A 120 and second site B 130 areequipped with the same applications such that the second site B 130 maytake over for the first site A 120 in the event of a failure. In otherfailover mechanisms, data is mirrored on both sites A and B 120, 130such that if a write occurs to a primary volume P of a first site A 120storage system 105, the write is mirrored to a secondary volume S in thesecond site B 130 storage system 107.

As mentioned above, this data replication across storage systems 105 and107 of the first site A 120 and second site B 130 is used as a way toprovide protection and continued access to the data for purposes ofdisaster recovery. If the primary volume P in the storage system 105 ofthe first site A 120 becomes unavailable for any reason, the failovermechanisms operate to transition work from the first site A 120 to thesecond site B 130. In known failover mechanisms, in order to make thetransition of work from the first site A 120 to the second site B 130 astransparent as possible without impacting the performance required bythe workloads being transitioned, the second site B 130 and itssecondary volume S in the storage system 107 are typically underutilizedduring normal, non-failover, operation of the first site A 120 inanticipation of a possible failover event. This ensures that the secondsite B 130 will have the resources and be able to meet the performancerequirements for handling the transitioned workloads from the first siteA 120, i.e. the primary workloads, in the event of a failure of thefirst site A 120 or primary volume P in storage system 105. However,this means that the significant resources of the second site B 130 arenot being used optimally.

The illustrative embodiments provide mechanisms for increasing theutilization of the second site B 130 and its secondary volume S in thestorage system 107 during normal, non-failover, modes of operation ofthe first and second sites A and 120, 130 while ensuring that the secondsite B 130 will provide the necessary resources for handlingtransitioned primary workloads from the first site A 120 in the event ofa failover occurring. The illustrative embodiments provide mechanismsfor specifying volume attributes in the second site storage controller150 for the local volumes L and secondary volumes S of the second sitestorage system 107, and priorities of workloads that permit non-criticalworkloads of the second site B 130 to be executed on designated localand secondary storage volumes L and S in the secondary storage 107during non-failover conditions.

In the event of a failover from the first site A 120 to the second siteB 130, these volume attributes and priorities may be utilized to controlthe allocation of secondary storage system 107 resources to primary andsecondary workloads such that the primary workloads are allocated therequired amount of resources to achieve the transition of the primaryworkload to the second site 130 with transparency and minimal, if any,impact to the performance of the primary workloads. In one illustrativeembodiment, this may involve defining storage volumes in the secondarystorage system 107 such that in the event of a failover occurring,certain storage volumes in the secondary storage system 107, such aslocal volume L, that are directed to handling non-critical workloads,i.e. workloads that are not part of the replication pair relationshipbetween the primary volume P in the first site A 120 and a secondaryvolume S in the second site B 130, are rendered non-usable during thefailover such that the resources of the second site B 130 storage system107 are made available to the primary workloads. In other illustrativeembodiments, the mechanisms of the illustrative embodiments implementthe priority settings of the first site A 120 on the second site B 130which applies them to both primary and secondary workloads. In this way,some of the non-critical workloads may still be able to be executed on asubset of the volumes in the second site B 130 storage system 107, e.g.,in the local volumes L, while primary workloads are given priority tothe remaining volumes, e.g., the secondary volumes S, of the second siteB 130 storage system 107.

FIGS. 3A and 3B are example block diagrams illustrating the use offailover mechanisms for increasing utilization of secondary storagesystems in accordance with one illustrative embodiment. FIG. 3Aillustrates the replication pair of a first site A 305 and a second siteB 360 as part of a peer-to-peer remote copy (PPRC), or other failovermechanism, prior to a failure of the first site A 305 in accordance withone illustrative embodiment. Here the term “replication pair” refers toan established relationship between two sites as a first site A 305 andsecond site B 360 where, in the event of a failure of the first site A305, workloads of the first site A 305 are migrated to the second site B360 and utilize the resources of the second site B 360 Which may includea copy of the applications/data matching the applications/data of thefirst site A 305. Elements associated with first site A 305 are referredto herein as the “primary” elements while elements associated with thesecond site B 360 are referred to herein as “secondary” elements.

FIG. 3B illustrates the replication pair of a first site A 305 and asecond site B 360 after a failure of the first site, in accordance withone illustrative embodiment. With a failover mechanism already in placebetween the first site A 305 and the second site B 360, in the event ofa failover condition occurring, workloads from the first site A 305 areredirected or transitioned from the first site A 305 to the second siteB 360. Such failover mechanisms are generally known in the art and thus,a more detailed explanation of the manner by which the workloads aretransitioned will not be provided herein. The present application isdirected to augmenting such failover mechanisms to permit maximumutilization of the secondary storage volumes of the storage system 330of the second site B 360 during normal, non-failover, modes of operationof the first site A 305 while ensuring availability to providesufficient resources for transparent transitioning of primary workloadsfrom the first site A 305 in the event of a rollover conditionoccurring.

With reference again to FIG. 3A, the second site storage system 330 ofthe second site B 360 comprises a plurality of logical storage volumes340-346 where each logical storage volume 340-346 has associated volumeattributes identifying priorities specifying the priority of types ofworkloads that are permitted to access the logical storage volume340-346. During normal, non-failover, modes of operation, the prioritiesassociated with the logical storage volumes 340-346 may be set to permitnon-critical workloads, e.g., local workloads 322 of the secondary siteB computing devices 320, to access or be serviced by all of, or amajority of, the logical storage volumes 340-346 of the secondary siteB′s storage system 330 that are sufficient to handle such localworkloads. This is contrary to known failover configurations in whichthe second site B′s storage system 330 remains unused with regard tolocal workloads waiting for a failover condition to occur causingprimary workloads to be transitioned from the first site A 305 to thesecondary site B′s storage system 330.

During this normal mode of operation, i.e. when the first site A 305 isnot experiencing a failure condition in either the primary sitecomputing devices 310 or in the primary storage system 370, the primaryworkloads 312 of the first site A 305 computing devices 310 may performinput/output (I/O) operations directed to the primary storage system 370with data replication or mirroring occurring to one or more of thelogical volumes 340-346 of the secondary storage system 330. These maybe separate logical volumes, for example a secondary volume 340 in FIGS.3A-3C, which are not accessible by local workloads 322 of the secondarysite computing devices 320. That is, certain logical volumes 340 in thesecondary storage system 330 may have associated volume attributesspecifying that the logical volumes 340 are only accessible by primaryworkloads 312 from first site A 305. As a result, these logical volumes342 only store data replicated or mirrored from the primary storagesystem 370 during normal modes of operation, or data modified by primaryworkloads 312 transitioned to the secondary storage system 330 duringfailover modes of operation. Other logical volumes 342-346 may haveassociated volume attributes indicating that these logical volumes342-346 are accessible by local workloads 322 during normal modes ofoperation. As a result, these logical volumes 342-346 may store dataused by local workloads 322 associated with secondary site computingdevices 320.

The secondary storage system 330 comprises a secondary storage systemcontroller 350 which includes a volume prioritization engine 352 thatoperates to control access of I/O operations to the various logicalvolumes 340-346 of the secondary storage system 330. The volumeprioritization engine 352 performs such control operations based on thevolume attributes associated with each of the logical volume 340-346 inthe secondary storage system 330 as well as volume prioritizationsettings 354 of the secondary storage system 330. The volume attributesspecify the priorities of workloads associated with the logical volumes340-346. The volume prioritization settings 354 associate prioritieswith different workloads and may further specify hierarchies of workloadpriorities and/or other settings to identify how to handle workloads ofvarious priorities with regard to access to logical volumes ofassociated secondary storage system 330.

That is, the volume prioritization engine 352 may store volumeattributes for each of the logical volumes 340-346 in the secondarystorage system 330. These volume attributes specify priority levels ofworkloads that are permitted to access the data stored in thecorresponding logical volume 340-346 during normal operation of thefirst site A 305. Thus, for example, a volume attribute for logicalvolumes 342-346 may specify that the logical volumes 342-346 are able tobe accessed by local workloads 322, while a volume attribute for logicalvolume 340 may specify that the logical volume 340 is not able to beaccessed by local workloads 322 and instead can only be accessed byprimary workloads 312 of a first site A 305. It should be appreciatedthat there may be various priority settings of various levels such thatthere may be multiple priority levels for the local workloads 322, forexample. These settings essentially identify which logical volumes340-346, if any, are able to be accessed by local workloads 322 of thesecond site B 360. In a simple example, the volume attributes may be ofthe type “critical” or “non-critical” to indicate whether thecorresponding logical volumes can be accessed by non-critical secondarysite workloads 322 during normal operation of the first site A 305.

In one illustrative embodiment, during normal operation, logical volumesare differentiated by those that have volume attributes of “critical”and those that are “non-critical.” For those logical volumes 342-346that have a “non-critical” volume attribute, local workloads 322 areable to utilize the resources of the second site B 360 to perform I/Ooperations on the data stored in these logical volumes 342-346. Forthose logical volumes 340 that have a “critical” volume attribute, localworkloads 322 are not able to access these logical volumes and onlyprimary workloads 312 are permitted to access these logical volumes 340.During normal operation, these primary workloads 312 may comprisepeer-to-peer remote copy mirroring or data replication operations, forexample. The logic of the volume prioritization engine 352 operatesduring normal operation based on these volume attributes and the volumeprioritization settings 354 which specify that for normal operation, topermit I/O operations from local workloads 322 to logical volumes havinga volume attribute of “non-critical” but to block local workloads 322from accessing logical volumes having a volume attribute of “critical.”

With reference now to FIG. 3B, in the event of a failover conditionoccurring in the first site A 305, a primary site computing device 310of the first site A 305, storage controller (not shown) of the primarystorage system 370, or the like, may issue a notification of thefailover condition to the secondary storage system controller 350. :Inresponse to the notification of the failover condition, the volumeprioritization engine 352 of the secondary storage system controller 350may operate to block local workloads 322 from accessing data of thelogical volumes 340-346 including those that have volume attributesspecifying that they may be accessed by local workloads 322, e.g.,logical volumes 342-346. As a result, the resources of the second site B360, e.g., processors, buses, storage devices, etc., are not utilized bythe local workloads 322 but are reserved for the primary workloads 312being transitioned to the second site B 360 as a result of the failovercondition occurring. Thus, during the failover mode of operation thesecondary storage system 330 of the second site B 360 providessufficient resources for supporting the transition of primary workloads312 from the first site A 305 to the second site B 360. This isillustrated in FIG. 3B by dashed line from the primary computing devices310 to the secondary storage system 330 and the “X's” over the logicalvolumes 342-346 which indicate that these logical volumes cannot beaccessed by local workloads 322 after the failover mode of operation hasbeen entered.

Should the failover condition be resolved, a notification may be sentfrom the primary site computing device 310, or storage controller of theprimary storage system 370, to the secondary storage system controller350. As a result, the mode of operation for the secondary storage system330 may be transitioned back from a failover mode of operation to anormal mode of operation. Thus, local workloads 322 may again accesslogical volumes 342-346 that have volume attributes specifying apriority which the local workloads 322 may access.

Thus, in a first illustrative embodiment of the present invention, localworkloads 322 of a second site B 360 may utilize the resources of thesecondary storage system 330 when they are otherwise not being utilizedby primary workloads 312 during normal operation of the first site A305. However, the mechanisms of the illustrative embodiments permit atransition of this operation to a failover mode of operation in whichlocal workloads are blocked and the full resources of the secondarystorage system 330 are provided for access by the primary workloads 312of the first site A 305. This ensures a transparent and minimalperformance impact transition of the primary workloads 312 to the secondsite B 360 during a failover while maximizing the utilization of thesecond site B 360 during normal operation.

During the failover mode of operation, because the local workloads 322are essentially blocked from accessing the logical volumes 342-346, theapplications submitting the local workloads 322 may fail if they are notable to meet the response requirements of the secondary site computingdevices 320. Once the failover condition has been rectified, theseapplications may be restarted on the secondary site computing devices320 and local workloads 322 my then be resubmitted to the logicalvolumes 342-346.

FIG. 3C is an example block diagram illustrating the use of failovermechanisms for increasing utilization of secondary storage systems inaccordance with another illustrative embodiment. As shown in FIG. 3C,rather than simply blocking local workloads 322 completely' during thefailover mode of operation, the primary workload priority settings 314used in the first site A 305 may be transmitted to the secondary storagesystem controller 350 along with the notification of the failovercondition having occurred. These primary workload priority settings 314may be merged with the existing volume prioritization settings 354 ofthe secondary storage system 330 to generate merged prioritizationsettings 358. This merging may result in a combination of the primaryworkload priority settings 314 and the volume prioritization settings354 of the secondary storage system 330 where any conflicts betweenpriority settings 354 may be resolved in favor of the primary workloadpriority settings 314. In other illustrative embodiments, the volumeprioritization settings 354 may be replaced entirely with the primaryworkload priority settings 314.

Based on the merged prioritization settings 358 of the secondary storagesystem 330, and the priority of the workloads (primary or secondary)submitting I/O requests to the secondary storage system 330, the volumeprioritization engine 352 may permit or deny I/O requests access to thevarious logical volumes 340-346 of the secondary storage system 330. Forexample, certain local workloads 322 may have priorities sufficientlyhigh to allow some resources of the secondary storage system 330 to beallocated to the local workloads 322 even when operating in a failovermode of operation. The priorities in the merged prioritization settings358 should be established to favor primary workloads 312 over all localworkloads 322. However, the priorities may be established such that someof the local workloads 322 may still have I/O requests serviced bycertain ones of the logical volumes 340-346.

For example, as shown in FIG. 3C, secondary volume 340 services I/Orequests from primary workloads 312 while local volumes 342 and 344service I/O requests from local workloads 322 having a next two highestpriorities below primary workload priority. A third priority level oflocal workloads 322 may have its I/O requests serviced by local volume346. In accordance with the merged prioritization settings 358, apriority scheme may be defined such that the primary workload priorityand the first two highest priority settings of local workloads may bepermitted to access corresponding logical volumes 340-344 of thesecondary storage system 330. However, in accordance with the mergedprioritization settings 358, local workloads having a priority of thethird priority level or lower may have their I/O requests blocked by thevolume prioritization engine 352, as illustrated in FIG. 3B by the “X”over local volume 342.

In either the illustrative embodiment shown in FIGS. 3A-3B or theillustrative embodiment shown in FIG. 3C, I/O requests from either theprimary workloads 312 or the local workloads 322 may be received by thevolume prioritization engine 352 of the secondary storage system 330.The volume prioritization engine 352 may determine whether the received110 requests should be permitted to be processed and, as a result,access the logical volume 340-346 that is targeted by the received I/Orequests. This determination may be based on the priority of theworkload submitting the I/O request, the volume attributes of the volumeto which the I/O request is targeted, and/or the volume prioritizationsettings 354, 358. With regard to the local workloads 322, during normalmode of operation, as long as the volume attributes of the targetedvolume are set such that the priority level of the local workload 322submitting the I/O request matches or exceeds the priority levelspecified in the volume attributes, then the I/O request is permitted toaccess the targeted volume. During failure mode of operation, in oneillustrative embodiment, all local workload I/O requests are blocked. Inanother illustrative embodiment, during failure mode of operation, localworkload I/O requests are blocked or permitted in accordance with volumeprioritization settings 354 or merged prioritization settings 358.

As a result, with the mechanisms of the illustrative embodiments, duringnormal modes of operation, the secondary storage system is permitted toallocated resources to local workloads, thereby increasing theutilization of the resources of the secondary storage system. Moreover,the mechanisms of the illustrative embodiments allow for prioritizationof workloads during failover modes of operation such that primaryworkloads of the primary site are prioritized over the local workloadsof the secondary site. This may involve blocking all I/O requests fromlocal workloads or allocating resources to local workloads based onassigned priorities and priority settings that provide preference toprimary workloads over all local workloads.

FIG. 4 is a flowchart outlining an example operation for implementing afailover mechanism in accordance with one illustrative embodiment. Theoperation outlined in FIG. 4 may be implemented in a storage controllerof a secondary storage system, for example.

As shown in FIG. 4, the operation starts with establishing volumeattributes specifying priorities of workloads that are able to accessthe various volumes (step 410). A determination is made as to whether afailure notification has been received from the first site (step 415).If a failure notification has been received, then a determination ismade as to whether the resources are constrained or not, i.e.determining if local access to the resources in response to a failure ofa primary site are to be constrained based on priority (step 417). Ifthe resources are constrained, then the mode of operation of the secondsite is switched to a failure mode in which secondary workload I/Orequests are blocked (step 420). Thereafter, if the resources are notconstrained, or if the failure notification has not been received, thensecondary workload I/O requests directed to storage volumes are received(step 425).

A determination is made as to whether the second site is currentlyoperating in a failure mode of operation (step 430). If so, then adetermination is made as to whether the resources are constrained (step437). If so, then the secondary workload I/O requests are blocked (step445). If the determination is that the second site is not currentlyworking in a failure mode of operation, or if the resources are notconstrained, then the volume attribute for the targeted storage volumeis checked (step 435) and a determination is made as to whether thevolume attribute allows secondary I/O requests to be processed for thetargeted volume (step 440). If not, then the secondary workload I/Orequest is blocked (step 445). If so, then the secondary workload I/Orequest is permitted to be processed by the targeted volume (step 450).

A determination is made as to whether the failure mode has been exited(step 455). If so, then the mode of operation of the secondary site ischanged to a normal mode of operation in which secondary workload I/Orequests are allowed to specified volumes (step 460). Thereafter, or ifthe failure mode has not been exited, then a determination is made as towhether operation of the illustrative embodiment s to be exited (step465). If not, the operation returns to step 415. Otherwise, theoperation terminates.

FIG. 5 is a flowchart outlining an example operation for implementing afailover mechanism in accordance with another illustrative embodiment.As shown in FIG. 5, the operation starts by establishing volumeattributes specifying priorities of workloads that are able to accessthe various volumes (step 510). Primary and secondary priority settingsare established for the storage systems of the first and second sitesstep 515). A determination is made as to whether a failure notificationhas been received from the first site (step 520). If a failurenotification has been received, then the mode of operation of the secondsite is switched to a failure mode in which priority settings of thefirst site are used in the second site step 525). The first sitepriority settings are merged with the secondary priority settings on thesecond site (step 530). Thereafter, or if the failure notification hasnot been received, then secondary workload I/O requests directed tostorage volumes are received (step 535).

In response to receiving the secondary workload I/O requests, a check ofthe volume attributes for the targeted storage volume is performed (step540). A check of the priority settings and the priority of the secondaryworkload is performed (step 545). A determination is made as to whetherthe I/O request from the secondary workload should be allowed (step550). If not, the secondary workload I/O request are blocked (step 555).If the I/O request from the secondary workload should be allowed, thesecondary workload I/O request is permitted to be processed by thetargeted volume (step 560).

Thereafter, a determination is made as to whether the failure mode hasbeen exited (step 665). Thereafter, if so, then the mode of operation ischanged to a normal mode of operation and the original security settingsof the secondary storage system are restored (step 570). A determinationis made as to whether the operation should be ended or not (step 575).If no, then the operation returns to step 520. Otherwise, the operationterminates.

As noted above, it should be appreciated that the illustrativeembodiments may take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements. In one example embodiment, the mechanisms of theillustrative embodiments are implemented in software or program code,which includes but is not limited to firmware, resident software,microcode, etc,

A data processing system suitable for storing and/or executing programcode will include at least one processor coupled directly or indirectlyto memory elements through a system bus. The memory elements can includelocal memory employed during actual execution of the program code, bulkstorage, and cache memories which provide temporary storage of at leastsome program code in order to reduce the number of times code must beretrieved from bulk storage during execution,

Input/output or I/O devices (including but not limited to keyboards,displays, pointing devices, etc.) can be coupled to the system eitherdirectly or through intervening I/O controllers. Network adapters mayalso be coupled to system to enable the data processing system to becomecoupled to other data processing systems or remote printers or storagedevices through intervening private or public networks. Modems, cablemodems and Ethernet cards are just a few of the currently availabletypes of network adapters.

The description of the present invention has been presented for purposesof illustration and description, and is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the art. Theembodiment was chosen and described in order to best explain theprinciples of the invention, the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

1. A method, in a data processing system comprising a storage systemcontroller and a secondary storage system, for controlling access tostorage volumes on the secondary storage system, comprising: associatingpriority values with a plurality of logical volumes in the secondarystorage system, wherein each logical volume has an associated volumeattribute specifying whether the corresponding logical volume may beaccessed by local workloads during the normal mode of operation.,associating second site priority values with one or more workloads inthe local workloads: determining, by the storage system controller,whether a first site computing device has sent a notification of afailure condition of a first site; and in response to a determinationthat the notification of the failure condition of the first site hasbeen received, modifying, by the storage system controller, a mode ofoperation of the second site from a normal mode of operation to afailure mode of operation, wherein in the failure mode of operation, thestorage system controller of the second site blocks requests from theone or more workloads in the local workloads having an associated secondsite priority value lower than a priority value associated with alogical volume targeted by the requests.
 2. The method of claim 1,wherein, in response to a failure condition of the first site occurring,a primary workload of the first site computing device is transitioned tothe second site such that the primary workload accesses the secondarystorage system during the failover mode of operation rather than aprimary storage system associated with the first site.
 3. The method ofclaim 1, further comprising in response to a determination that thenotification of the failure condition of the first site has not beenreceived, permitting, by the storage system controller, local workloadsof a second site computing device to access storage volumes on thesecondary storage system in the normal mode of operation.
 4. The methodof claim 3, wherein at least one first logical volume in the pluralityof logical volumes has a corresponding volume attribute specifying thatthe at least one logical volume cannot be accessed by local workloadsduring the normal mode of operation, and wherein at least one secondlogical volume in the plurality of logical volumes has a correspondingvolume attribute specifying that the at least one logical volume can beaccessed by local workloads during the normal mode of operation.
 5. Themethod of claim 1, wherein, in the failure mode of operation, thestorage system controller blocks all requests from local workloadsdirected to all logical volumes of the secondary storage system. 6.(canceled)
 7. The method of claim 1, wherein modifying, by the storagesystem controller, a mode of operation of the second site from a normalmode of operation to a failure mode of operation comprises obtainingfirst site priority values for at least one of workloads or logicalvolumes from the first site and integrating the first site priorityvalues into the second site priority values.
 8. The method of claim 7,wherein integrating the first site priority values comprises merging thefirst site priority values with the second site priority values togenerate merged priority values, and applying the merged priority valuesto requests from the local workloads to determine which, if any,requests from workloads in the local workloads to block.
 9. The methodof claim 7, wherein integrating the first site priority values comprisesreplacing the second site priority values with the first site priorityvalues and applying the first site priority values to requests from thelocal workloads to determine which, if any requests from workloads inthe local workloads to block.
 10. The method of claim 1, furthercomprising: determining, by the storage system controller, whether afirst site computing device has sent a notification of a discontinuationof a failure condition of the first site; and in response to anotification of a discontinuation of a failure condition of the firstsite being received by the storage system controller, discontinuing theblocking of at least a portion of the requests from local workloads ofthe second site computing device.
 11. A computer program productcomprising a non-transitory computer readable storage medium having acomputer readable program stored therein, wherein the computer readableprogram, when executed on a storage system controller associated with asecond site in a replication pair comprising a first site and the secondsite, causes the storage system controller to: associate priority valueswith a plurality of logical volumes in the secondary storage system,wherein each logical volume has an associated volume attributespecifying whether the corresponding logical volume may be accessed bylocal workloads during the normal mode of operation:, associate secondsite priority values with one or more workloads in the local workloads:determine whether a first site computing device has sent a notificationof a failure condition of a first site; and in response to adetermination that the notification of the failure condition of thefirst site has been received, modifying a mode of operation of thesecond site from a normal mode of operation to a failure mode ofoperation, wherein in the failure mode of operation, the storage systemcontroller blocks requests from the one or more workloads in the localworkloads having an associated second site priority value lower than apriority value associated with a logical volume targeted by therequests.
 12. The computer program product of claim 11, wherein, inresponse to a failure condition of the first site occurring, a primaryworkload of the first site computing device is transitioned to thesecond site such that the primary workload accesses the secondarystorage system during the failover mode of operation rather than aprimary storage system associated with the first site.
 13. The computerprogram product of claim 11, wherein in response to a determination thatthe notification of the failure condition of the first site has not beenreceived, the storage system controller permits local workloads of asecond site computing device to access storage volumes on the secondarystorage system in the normal mode of operation.
 14. The computer programproduct of claim 13, wherein at least one first logical volume in theplurality of logical volumes has a corresponding volume attributespecifying that the at least one logical volume cannot be accessed bylocal workloads during the normal mode of operation, and wherein atleast one second logical volume in the plurality of logical volumes hasa corresponding volume attribute specifying that the at least onelogical volume can be accessed by local workloads during the normal modeof operation.
 15. The computer program product of claim 11, wherein, inthe failure mode of operation, the storage system controller blocks allrequests from local workloads directed to all logical volumes of thesecondary storage system.
 16. (canceled)
 17. The computer programproduct of claim 11, wherein modifying, by the storage systemcontroller, a mode of operation of the second site from a normal mode ofoperation to a failure mode of operation comprises obtaining first sitepriority values for at least one of workloads or logical volumes fromthe first site and integrating the first site priority values into thesecond site priority values.
 18. The computer program product of claim17, wherein integrating the first site priority values comprises mergingthe first site priority values with the second site priority values togenerate merged priority values, and applying the merged priority valuesto requests from the local workloads to determine which, if any,requests from workloads in the local workloads to block.
 19. Thecomputer program product of claim 17, wherein integrating the first sitepriority values comprises replacing the second site priority values withthe first site priority values and applying the first site priorityvalues to requests from the local workloads to determine which, if anyrequests from workloads in the local workloads to block.
 20. Thecomputer program product of claim 11, wherein the computer readableprogram further causes the storage system controller to: determinewhether a first site computing device has sent a notification of adiscontinuation of a failure condition of the first site; and inresponse to a notification of a discontinuation of a failure conditionof the first site being received by the storage system controller,discontinuing the blocking of at least a portion of the requests fromlocal workloads of the second site computing device.
 21. An apparatus,comprising: a storage controller of a secondary storage system in asecond site in a replication pair comprising a first site and the secondsite; and a memory coupled to the processor, wherein the memorycomprises instructions which, when executed by the storage controller,cause the storage controller to: associate priority values with aplurality of logical volumes in the secondary storage system, whereineach logical volume has an associated volume attribute specifyingwhether the corresponding logical volume may be accessed by localworkloads during the normal mode of operation, associate second sitepriority values with one or more workloads in the local workloads:determine whether a first site computing device has sent a notificationof a failure condition of the first site; and in response to adetermination that the notification of the failure condition of thefirst site has been received, modifying a mode of operation of thesecond site from a normal mode of operation to a failure mode ofoperation, wherein in the failure mode of operation, the storagecontroller blocks requests from the one or more workloads in the localworkloads having an associated second site priority value lower than apriority value associated with a logical volume targeted by therequests.
 22. The method of claim 21, wherein modifying, by the storagesystem controller, a mode of operation of the second site from a normalmode of operation to a failure mode of operation comprises obtainingfirst site priority values for at least one of workloads or logicalvolumes from the first site and integrating the first site priorityvalues into the second site priority values.